Garden Detective: Law on lawn fertilizer

I was quite surprised to notice on your March calendar that it is illegal to fertilize your lawn in Nassau and Suffolk before April 1. Can you explain why? -Ken Wenthen, West Hempstead

Nassau and Suffolk both have banned fertilizer use during the winter to limit nitrogen pollution in local groundwater. In Suffolk, lawns may not be fertilized between Nov. 1 and April 1; Nassau's ban applies from Nov. 15 through April 1.

Plants can't absorb fertilizers when they are dormant or about to go dormant, or when the ground is frozen, so the excess nitrogen and phosphorus runs off into the groundwater and eventually makes its way to the water table. The fertilizer you intended to benefit your lawn ends up fertilizing waterside plants along bays, streams and rivers, disrupting the delicate ecosystems there, causing smaller, less dominant species and weeds to grow out of proportion and choke out beneficial plants. That messes with the food chain and triggers harmful algae blooms. On a more personal level, money spent on fertilizer in late fall or early spring would be going to waste as it won't benefit your lawn, anyway.

For a natural alternative to synthetic fertilizers all season long, simply remove the bag from your mower and allow grass clippings to remain on the lawn. They'll break down into a safe, compatible form of nitrogen. If you really must fertilize, follow package directions carefully and remember less is more.

I planted basic lilac bushes about three years ago when I purchased my house. The first year the bushes bloomed fully. The past few years, I haven't been so lucky. They get partial shade/sun, and I do give them fertilizer each spring. Is there something I'm doing wrong? Should I prune them down? If so what do I use, and when do I prune? Thank you! --Kerrie Huser, Mount Sinai

The problem could be one of two things: Lilacs need full sun in order to bloom to their full potential, so your partial shade conditions could be to blame. Also, applying too much nitrogen fertilizer will force the plants to put most of their energy into growing in size, leaving little left for blooming. I would skip the fertilizer this year and see what happens. If your plants still don't bloom properly, trim nearby trees and/or shrubs to increase their exposure to sunlight; if that isn't possible, move them next year in late winter or early spring, while they're still dormant. Good luck!

I read that you are recommending just run-of-the-mill fertilizers for fruit trees. Yet, I am under the impression that special fertilizers, with certain micronutrients, are needed to ensure healthy trees. All these years, I have been buying these specialized fruit tree fertilizers. I would appreciate your thoughts on the subject. --Tom Smith,  Jamesport

The best fertilizer for fruit trees is a generous helping of horse manure. If you don't live near a stable or are unable to locate any, then any general purpose balanced fertilizer (5-10-10) will do in most cases.